U.S. Pat. No. 3,860,862 discloses a method for following an optical line for positioning a metal cutting tool with respect to the surface of a workpiece for forming a feature in the workpiece. The process is carried out by use of X,Y,Z drive systems under the control of logic circuits, binary counters and other control components which follow an optical tracer to control the drive systems to replicate a traced pattern in the workpiece.
U.S. Pat. No. 3,986,767 discloses an optical focusing apparatus wherein a beam of collimated energy is focused on the surface of a workpiece to form a feature therein. While the apparatus varies the position of a focal point on the workpiece it requires movement of the whole laser nozzle head along multiple axes by use of servo motors and drive screw systems.
U.S. Pat. Nos. 3,392,259; 4,389,561; 4,406,940; 4,540,869 and 4,733,048 all disclose laser head apparatus with lens components for focusing laser energy on a work surface.
None of the aforesaid references disclose a method for trepanning parts by a process which varies the trepanning diameter without shifting a laser head by use of the normal multiaxis drive systems of such machining apparatus.